Full Length Research Paper

Optimization of the industrial production of bacterial a-amylase in Egypt. V. Analysis of kinetic data for enzyme production by two strains of Bacillus amyloliquefaciens

F. Mohammad ¹, O. El-Tayeb²* and M. Aboulwafa³

¹Department of Chemical Engineering and Pilot Plant, National Research Centre, Egypt.

²Department of Microbiology and Immunology, Faculty of Pharmacy, Cairo University, Egypt.

³Department of Microbiology and Immunology, Faculty of Pharmacy, Ain Shams University, Egypt.

*Corresponding author. E-mail: omtayeb@link.net.

Accepted 19 October, 2007

A kinetic study was conducted for a-amylase production process in shake flasks by the wild type strain of Bacillus amyloliquefaciens (strain 267) and in the fermentor by the amplified variant of the same organism (strain 267CH). a-Amylase was produced concurrently with growth up to about 72 h, after which it continued without increase in biomass and, in the case of strain 267 even after biomass declined. Application of logistic, Luedeking-Piret and the modified Luedeking-Piret mathematical models to the kinetic data revealed that a-amylase production in both cases occurred through both growth- and non-growth associated mechanisms and that the amount of enzyme produced through non-growth associated mechanism exceeded that produced through growth associated mechanism by 3.5 and 2.3 fold by strains 267 and 267CH, respectively. Although with both strains substrate consumption continued even after growth leveled, the application of the model revealed that the major portion of substrate consumption occurred during growth but that a considerable amount was also consumed after maximum growth was reached, mainly for enzyme production. In the bioreactor, increasing aeration from 1 to 2 vvm increased the overall specific growth rate, the production rate, the specific production rate, and the specific substrate consumption rate and also shortened the time necessary for maximum production of both biomass and enzyme. The increase in biomass either by prolonging the incubation time or by increasing aeration was accompanied by an increase in enzyme production. However, even after maximum biomass was reached, enzyme production still continued to increase, under both conditions.

Key words: Production kinetics, process modeling, fermentation, bacterial amylase, biotechnology.